A. Detergents
Detergents are substances used to remove soil from materials with water. Since detergents are used under such different conditions, e.g., type of soil, material to be cleaned, water temperature, etc., it is not surprising that many different types of detergents are available. One class of detergents are the bar soaps, liquid soaps, and liquid shampoos used for personal cleaning. A second class of detergents are the "light-duty" liquids and powders used for dishwashing and miscellaneous household cleaning. A third class of detergents are the "heavy duty" liquids and powders primarily used for cleaning clothes in washing machines.
All detergents contain at least one surfactant. A surfactant is a substance whose molecules contain both hydrophilic and oleophilic groups. The surfactants are primarily responsible for the soil-removing properties of the detergent, although many other components of the detergent augment the surfactants. Surfactants are routinely classified according to their electrostatic charge: the nonionics possess no net electrostatic charge, the anionics possess a negative charge, the cationics possess a positive charge, and the atmospherics possess both positive and negative charges.
Most detergents, contain many other substances in addition to the surfactants. Some detergents contain builders which aid the soil-removing properties of the surfactants in several ways. In particular, builders help prevent the formation of insoluble soap deposits, aid in soap suspension, and help prevent the precipitation of certain calcium and magnesium salts. Some detergents employ hydrotropes to reduce their viscosity and to prevent phase separation. Fillers are used in some detergents to control density and improve flow properties. Many heavy-duty detergents contain anti-redeposition agents to help prevent redeposition of soil on the clothes. Other ingredients commonly found in detergents are perfumes, corrosion inhibitors, pH adjusters or buffers, dyes or colorings, optical brighteners, foam control agents, bleaches, opacifiers, and stabilizers.
Most types of detergents are sold both as powders and as liquids. Although some powders are prepared by mixing together dry ingredients, the vast majority of powders are prepared by drying an aqueous slurry of ingredients. The popularity of the liquids continues to increase, primarily because of their convenience to the consumer, but also because of the savings in eliminating the drying step. However, the powdered heavy-duty detergents still outsell the liquid heavy-duty detergents because there continues to be difficulty in formulating a heavy-duty liquid which cleans as well as a powder. The powders generally contain rather large amounts of builders to improve the performance of the surfactants. Unfortunately, the most effective builders have relatively low water solubilities and are used, if at all, in relatively small amounts in the liquids. To compensate for the absence or low level of builder, detergent manufacturers have tried to increase the level of surfactants in the liquids. However, the level of surfactants is limited by viscosity and problems of phase separation. Many detergent manufacturers have attempted to improve the physical properties of their heavy-duty liquids by including hydrotropes in their formulations.